In a known manner, a flywheel via its mechanical rotation is used in a device for the temporary storage of energy that has an application in many fields, such as in the storage and the smoothing of intermittent renewable energies of the wind, solar type, the supplying of isolated sites with electricity, the restitution of energy for the braking of vehicles, etc.
With regards to other devices for the storage of electrical energy such as electric batteries, the flywheel has the main advantage of a practically unlimited service life, implying over time a lower cost of energy storage than with the other devices.
A flywheel comprises a solid body, usually referred to by the term “mass”, linked to the rotating shaft of an electric motor. The electric motor drives the flywheel in rotation which can reach very high rotation speeds in a few minutes, even in a few seconds. After the stopping of the supply of the electric motor, the mass of the flywheel having stored kinetic energy continues to rotate and can then return mechanical energy which is in turn converted into electrical energy by using the motor as an electric generator.
The centrifugal force that the mass of the flywheel is subjected to results in very high traction stress for the material that comprises the mass. As such it is necessary to choose a manufacturing material that exhibits a high resistance to traction, in particular resistant to at least 100 MPa.
Today, the mass of a flywheel is manufactured most often from steel and for a few years now from carbon fibres.
However, due to its high cost price, in particular due to the material that comprises it, the flywheel is often set aside in order favour other types of energy storage devices such as electric batteries.